Perl's versatile split function
I love Perl’s split function. Far more powerful than its feeble cousin join, split has some wonderful features that should make it a regular feature of any Perl programmer’s toolbox. Let’s look at some examples.
Split a sentence into words
To split a sentence into words, you might think about using a whitespace regex pattern like /\s+/
which splits on contiguous whitespace. Split will ignore trailing whitespace, but what if the input string has leading whitespace? A better option is to use a single space string: ' '
. This is a special case where Perl emulates awk and will split on all contiguous whitespace, trimming any leading or trailing whitespace as well.
my @words = split ' ', $sentence;
Or loop through each word and do something:
use 5.010;
say for (split ' ', ' 12 Angry Men ');
# 12
# Angry
# Men
The single-space pattern is also the default pattern for split
, which by default operates on $_
. This can lead to some seriously minimalist code. For example if I needed to split every name in a list of full names and do something with them:
for (@full_names)
{
for (split)
{
# do something
}
}
And who says Perl looks like line noise?
Create a char array
To split a word into separate letters, just pass an empty regex //
to split:
my @letters = split //, $word;
Parse a URL or filepath
It’s tempting to reach for a regex when parsing strings, but for URLs or filepaths split
usually works better. For example if you wanted to get the parent directory from a filepath:
my @directories = split '/', '/home/user/documents/business_plan.ods';
my $parent_directory = $directories[-2];
Here I split the filepath on slash and use the negative index -2
to get the parent directory. The challenge with filepaths is that they can have n depth, but the parent directory of a file will always be the last but one element of a filepath, so split
works well.
Extract only the first few columns from a separated file
How many times have you parsed a comma separated file, but didn’t want all of the columns in the file? Let’s say you wanted the first 3 columns from a file, you might do it like this:
while <$read_file>
{
my @columns = split /,/;
my $name = $columns[0];
my $email = $columns[1];
my $account = $columns[2];
...
}
This is all well and good, but split
can return a limited number of results if you want:
while <$read_file>
{
my ($name, $email, $account) = split /,/;
...
}
Or to revisit an earlier example, splitting on whitespace:
for (@full_names)
{
my ($firstname, $lastname) = split;
...
}
Conclusion
These are just a few examples of Perl’s versatile split
function. Check out the official documentation online or via the terminal with $ perldoc -f split
.
This article was originally posted on PerlTricks.com.
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David Farrell
David is a professional programmer who regularly tweets and blogs about code and the art of programming.
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